Method for improving the imaging properties of a projection objective for a microlithographic projection exposure apparatus

A method for designing a projection objective of a microlithographic projection exposure apparatus, in which an illuminated mask is projected by the projection objective onto a photosensitive layer, said method comprising:

• a) determining, by simulation, locations in an exit pupil of the projection objective which are illuminated by projection light during a projection of the mask;
• b) determining, for at least one image point of the projection objective, a simulated value of an imaging quantity at least at the locations determined according to step a), wherein the imaging quantity influences the imaging properties of the projection objective;
• c) calculating measures such that the simulated value of the imaging quantity approximates a desired value of the imaging quantity at the locations determined according to step a), wherein deviations of the simulated value from the desired value are taken into account exclusively at the locations determined according to step a);
• and
• d) designing the projection objective according to the measures calculated in step c).

A microlithographic projection exposure apparatus for imaging a mask onto a photosensitive layer, comprising:

• a) a projection objective having an exit pupil,
• b) a measuring device for measuring, for at least one image point of the projection objective, a value of an imaging quantity at least at locations in the exit pupil which are illuminated by projection light during a projection of the mask, wherein the imaging quantity influences the imaging properties of the projection objective;
• c) a comparator which compares the measured value with a desired value for the imaging quantity;
• d) a correcting device which implements corrective measures such that the at least one measured value approximates the desired value, wherein deviations of the measured value from the desired value are taken into account exclusively at the locations illuminated in the exit pupil.